Method and apparatus for the burning of mineral sulphides in gaseous suspension



/A/l/E/VTORS.

ATTORNEY Aug. 10, 1937. B. A. s'nMMEL ET AL METHOD AND APPARATUS FOR THEBURNING OF MINERAL SULPHIDES IN GASEOUS SUSPENSION Filed July 29, 1935BYRON ,4A/60.5 ST/MMEL. fri/vA/ETH 00A/wv MCB/SAN.

GRAHAM cRU/cmsHAN/f.

Patented Aug. l0, 1937 UNITED STATES PATENT OFFICE METHOD AND APPARATUSFOR THE BURN- ING OF MINERAL SULPHIDES IN GASEOUS SUSPENSION tion ofCanada Application July 29, 1935, Serial No. 33,652

7 Claims.

Our invention relates to an improved method and apparatus for theroasting of mineral sulphides in gaseous suspension, and is particularlydirected toward eiecting a positive control over the amount of sulphatesand sulphur in the final product.

In our United States Patents 1,884,348 and 1,963,282 we disclosed amethod and apparatus for roasting mineral sulphides of zinc, iron,copper and lead, either singly or in combination, in gaseous suspension,characterized in that the charge, in a finely divided state, is' blowninto the combustion chamber and is disseminated, concurrently with theair blast through it, for the exposure of each particle to the oxidizingaction of the air. The roast is effected exclusively by the combustionof the sulphur content of the charge, supported by the air blast, forconverting the sulphides into oxides, some sulphates and sulphurdioxide. The temperature and time period of the roast are regulated forpromoting the oxidation of the charge without fusion or incipientfusion, and with the formation of a minimum amount of ferrates whentreating zinc sulphides containing iron. The roasted material settlingat the bottom of the combustion chamber is removed for furtherprocessing, and the gaseous products of combustion are evacuated fromthe combustion chamber having a high concentration of sulphur dioxide.

Among the principal features of our invention are the improvementscorrelated to the method and apparatus disclosed in the principalpatents whereby we may effect at all times a positive a control over theamount of sulphates and sulphur in the nal product.

The type of roast to which mineral sulphides are subjected is largelydependent on the subsequent processes by means of which the metal isseparated from its diluents and recovered. For example in roasting zincsulphides to form zinc oxide for the subsequent leaching andelectrolytic extraction of the zinc, it is generally economical to havesufficient soluble sulphur present with the productsof combustion tosupplement the acid for theiosses occurring during the leaching andelectrolyzing steps.

In the roasting of mineral sulphides for the manufacture of acid and/orone of the various reduction "processes, however, it is not onlydesirable but necessary to obtain as complete elimination of sulphatesand sulphur as possible for the economical and efcient operation of thesubsequent processes.

It is also desirable in certain instances to ob- (Cl. 'l5-9) tain morethan one product, each recoverable separately. An example of this is inthe production of lithopone in conjunction with the separation andrecovery of zinc by the retort process, wherein it is desirable in theproduction of lithopone to recover a highly soluble sulphate product,and in the preparation of the sulphides for the retort reduction processit is necessary to have as complete elimination of sulphur as possible.

In roasting in suspension, the burning hearth, which has a collectinghearth and rabbling device at its base, is maintained preferably withinthe temperature range of from 1650 to 1700 F. which precludes theformation and existence of metallic sulphates, such as zinc and iron, sothat most of the metallic sulphates which are collected on or returnedto this hearth would be decomposed to oxides. Any metallic oxideparticles, however, which are carried out of the combustion chamber bythe exit gases are subjected to the sulphatizing action of those gasesand, depending on the temperature and the length of time before theparticles are removed from the gases, form varying amounts of sulphates.

We have found that the operation of the process disclosed in thehereinbefore mentioned patents, and in fact any of the processes inwhich mineral sulphides are burned in gaseous suspension, is readilyadaptable to a method for effecting a positive control over the amountof sulphates formed.

We have found also that if part or all the solid products of combustionfrom the furnace is rabbled in a sulphur dioxide atmosphere at atemperature below the decomposition temperature of the sulphates,preferably about 900 F. in the case of zinc sulphate, sulphatizingaction takes place rapidly and, depending on the length of time thematerial is exposed to and the concentration of the sulphur dioxide inthe gases, regulated amounts of sulphate sulphur may be formed in theroasted product, dependent on the subsequent processes for which thematerial is desired.

The manner in which We attain the objects of our invention is by theaddition of one or more sulphating chambers located below the combustionchamber and communicating therewith in such a manner that all or anydesired part of the oxide particles can be diverted to drop into thesulphating chamber and on to a settling hearth forming the lower part ofthe sulphating chamber whereon they are rabbled to expose each particleto the sulphatizing action of sulphur dioxide bearing gases, while thetemperature of the sulphating chamber is maintained below thedecomposition temperature of the sulphates formed. 'I'he sulphatingchamber is also adapted to receive exit gases evacuated'from theroasting 6 chamber and evacuate 'the same for further processing orreturn them to the combustion chamber.

As a further feature we provide a system of conveyors whereby the dustparticles separated 10 from the evacuated gases in thevarious'dustcollecting chambers may be returned to the combustionchamber to result in a product substantially free from sulphates andsulphur, or to the sulphating chamber to result in a highly solublesulphate product. or eliminated from the process altogether. A furtherconveyor system is provided to carry away the products of the sulphatingchamber.

A complete understanding of our -invention may be had from the followingdescription and accompanying drawing in which:

' Fig. lis-arvertical cross sectional view of the furnace, in which theassociated parts suitable for carrying out our method are showndiagrammatically.

Fig. 2 is a vertical cross sectional view of the lower portion ofthefurnace when more than one sulphating chamber is used.

Referring to the drawing, in which like characters of reference refer tolike parts throughout the specification and drawing, the preferredembodiment of our invention herein disclosed may be correlated with themethod and apparatus discl'ised in the principal Patents 1,884,348 and.35 1,963,282 respectively, it will only be necessary to refer to theprincipal parts of that apparatus in i order to obtain a completeunderstanding of our improvement.

'I'he shaft furnace I has drying hearths: 2 and 40 5 located at the top,the drying hearth 2 communicating with the hearth 5 by means of thedrop-holes 3 spaced at "regular intervals about the vertical rotatingshaft 4.

'I'he combustion or roasting chamber 8 is of large cross sectional areaand of relatively great depth, so proportioned that the nely dividedmineral sulphides blown into the upper portions thereof have ample roomfor free dispersal throughout the chamber area for unimpeded downwardmovement therethrough in an oxidizing atmosphere to permit the completeloxidation of the mineral sulphides in gaseous suspension.

The settling hearth 9 at the bottom of the chamber 8 has a circularopening Ill., forming an annular opening around the insulating casing 1of the central shaft 4, which communicates withl the hearth II.

A conduit I6 communicates with the drying hearth 5 and the grinding millor other suitable pulverizing apparatus I1. The conduitv I8 communicateswith the mill I1 and hopper I9.. 'I'he conduit 30 communicates with thehopper I9 and the nozzle 26 through which the pulverized material'isblown into the combustion chamber 8 i concurrently with a blast of air.N Gas is evacuated from the combustion cham- .ber and settling hearthsthrough the gas conduit .21Uand, after passing through suitabledust-colvyo-lecting apparatus, is withdrawn from the process forsubsequent treatment, or, if desired, part thereof may be returned tothe combustion chamber to maintain the temperature of that chamberWithin the desired limits to prevent fusion or 75 incipient fusion ofthe particles.

Theconduits I3 and I4 communicate with the .settling hearths 9 and IIrespectively and provide means for separately evacuating the roastedmaterial settling on those hearths vto the storage bln I5.

The vertical rotating shaft 4 has mounted thereon rabble arms A, B, Cand D moving on the hearths 2, 5, 9 and I I respectively, the rabblesbeing so adjusted as to rabble the particles towards and into thedrop-hole 3 and conduits I6, I3 and I4 respectively.

Referring now to the parts relating to our improvement, we have addedbelow the hearth I I an additional hearth 51, and forming the sulphatingchamber therebetween, preferably constructed of cast iron or steel, andhaving a lute ring 10 to seal the opening between the hearth andtheinsulating casing 1 of the shaft 4.

The hearth II communicates with the hearth 51 by means of the drop-hole65, which is provided with the valve member 15, through which theroasted material may drop into the sulphating chamber and on tothehearth 51. Hot sulphur dioxide bearing gases are introduced into thesulphating chamber through the openings 69 spaced at regular intervalsabout the vertical rotating shaft 4.

Rabble arms 58 are secured to the rotating shaft 4, the rabbles being sopositioned as to agitate the material on the hearth 51 to expose eachparticle to the sulphatizing action of the gas, and rabble the materialfrom the periphery of the hearth to the drop-hole 66 through which itdrops on to the conveyor 61, which conveys it to a suitable storage binor to further treatment.

The opening 65 in the hearth II is provided with suitable adjustableclosure means such as the valve 15 which, when adjusted in conjunctionwith the valves 12 and 13 provided in the conduits I4 and I3respectively, all or any desired percentage of the material on thehearth II may be directed into the conduits I3 and I4 or on to thehearth 51. n

'I'he gas in the sulphating chamber is evacuated through the gas conduit59 'which is provided with a valve 6I) to control the rate ofevacuation. The gas conduit 59 communicates with the main gas conduit 21which directs the flow of the gases into suitable dust-collectingchambers wherein the dust particles are separated from the gases.

The conveyor 62 which conveys the dust particles from thedust-collecting chambers to the hearth 51 also communicates with theelevator 63 and conveyor 6.4, whereby the dust may be' returned to thecombustion chamber rather than the sulphating chamber as desired. Theconveyor 62 also communicates with the conveyor 61 by means of which thedust may be withdrawn entirely from the process.

The .gas conduit 21 is further provided with a valve 6I located betweenthe conduit 59 and the combustion chamber by means of which all or anydesired percentage of the gaseous products of combustion may be directedfrom the combustion chamber through the openings 69 into the sulphatingchamber. A

The method of operating the process depends on the subsequent processesfor which the final products are desired. For example in the treatmentof zinc sulphides when the final product is desired for a zinc reductionor retort process, a grade of product is required which is low insuiphates and total sulphur. All the products collected in the ilues,dust-collectors, etc., are returned to the hearth at the base of thecombustion chamber 8 by way oi the conveyor 62, the elevator 63 and theconveyor 6l, being introduced into 'the combustion chamber on theperiphery of the settling hearth 9. Here it quickly attains theprevailing temperature oi.' from 16501700 F. and, along with thematerial already collected on this hearth, israbbled inwardly across thehearth with the result that' the most important sulphates, such as thoseof zinc and iron, are rapidly 1o decomposed into oxides, sulphur dioxideand oxygen. To ensure that this reaction will go to completion and toeliminate any residual sulphide i or sulphate sulphur, the material isdropped through the opening l0 on to the hearth I I where it is rabbledoutwardly and discharged i'rom the periphery into the conduit I4substantially free of sulphates and sulphur.

During this operation the valve 15 in the drophole 65 is closed and thevalve 'I2 leading into the conduit 'Il is opened to permit the freeevacuation of the roasted material from the process. 'Ihe valve 60 inthe gas conduit 59 is closed and the valve 6I in the main gas conduit 21is opened wide to permit the free ow oi the gaseous products ofcombustion from the combustion chamber.

'Ihe operation of the furnace is readily adaptable to produce a highlysoluble sulphate product as required, for example, in the manufacture oflithopone or for the production of zinc sul'- phate. This productresults from an easily executed regulation of the ow of the gases fromthe combustion chamber, together with the diversion of the productscollected on the settling hearths 9 and II. If the highest degree oisulphation is desired all the roasted products of the suspensionburning, together with the ilue dust collected in the variousdust-collecting chambers, are introduced into the sulphating chamberthrough the drop-hole 65 in the hearth Il, the valves 12 and 'I3 in theconduits i4 and I3 being closed to prevent the ow of materialtherethrough and the valve 15 opened, and the iiue dust by way of theconveyor 62. -The material settles on the periphery of the hearth 51and, by means of the rabbles secured to the rabble arms 58, is rabbledinwardly across the hearth toward and into the drop-'hole 66, duringwhich rabbling each particle is exposed to the sulphatizing action ofthe sulphur dioxide bearing gases from`the 'combustion chamberintroduced through the openings 69 of the hearth Ii. By regulating thevalve 60 in the gas conduit 59 and the valve 6| in the main gas conduit21 a suiiicient volume of gas is diverted into the sulphating chamber tomaintain the temperature of that chamber within the range wherein thehighest degree of sulphation will be eiected. We prefer to maintain thetemperature of the sulphating chamber about 900 although we do not wishto conne ourselves to that temperature'.

Under these conditions, especially in the .presence of iron in the formof ferrie oxide which aids catalytically to form metallic sulphates, thematerial rapidly becomes sulphated and when the nal product is nallydischarged from the hearth through the drop-hole 66 on to the conveyor61 it is in a highly sulphated condition and is an ideal product forfurther processing.

The above two examples illustrate the pro- 70 cedure followed to obtaina single product. -We have found it possible in the operation of ourmethod to obtain more than one` product, each recoverable separately,ready for further separate processing. An example where two products aredesired from one operation is in the preparation of zinc sulphides i'orreduction by the retort process wherein it is necessary that aminimum-oi sulphates and sulphur is; present in the ilnished product,operated in conjunction with a process oi' the conveyor 62. Byregulating the valves 60 15 and 6I in the gas conduits 59 and 21 thenecessary volume oi gases is diverted from the combustion chamber to thesulphating chamber to maintain the temperature of that chamber withinthe desired limits. The material is rabbled in- 20 wardly across thehearth 51 nally reaching the drop-holes 66 to drop on to the conveyor 61a highly sulphated' product suitable for further processing.

The remainder of the dust products are di- 25 verted to the elevator 63and conveyor 64 by means of which they are returned to the combustionchamber 8 on the periphery of the settling hearth 9. Here it is mixedwith the other materm settling on this hearth and is rabbled in- 30wardly acrossthe hearth to the opening I0 to drop on to the hearth ii,being nally discharged ,from the furnace through the conduit i4. Duringits progress across the hearths 9 and il the material is raised to theprevailing tempera- 3v" ture, about 1700 F., at which temperature themetallic sulphates could not exist as such, and when discharged from thefurnace is substantially free from sulphates and sulphur.

While this example illustrates the operation of 4" the method to obtaintwo products when the amount of sulphate sulphur desired is less thanthe amount of nue dust available it win be apparent that should moresulphates be desired than there is flue dust available all the flue dust45 can be returned to the sulphating hearth 51 and any deiiciency madeup by diverting part of the roasted material from the hearth Il throughtlfe drop-hole 65 by adjustment ofthe valve 15 and the valves 12 and 13to result in any. desired per- 50 centage -of the roasted material beingconverted into sulphates,'bo th sulphates and oxides being recoverableseparately.

In the operation of our improved method wehave found it possible toretain all the features 55 of the principal method in that the roast isconducted exclusively by the combustion of the sulphur content of thecharge without the use of extraneous fuel; the quick removal of theroasted products from the high temperature of 60 the combustion chamberminimizes the formation of ferrates when the charge contains iron inaddition to zinc; and fusion or incipient fusionis prevented byregulating thetemperature'of the combustion chamber. s f

In the operation Voi? our process, it will be clearly understood, ofcourse, that the temperature range within which the sulphating chamberis maintained is dependent on the type of charge 70 being treated andthe degree of sulphation desired and, in the case of zinc, while zincsulphates will form at any temperature below say 1400" F. thedecomposition temperature of zinc sul'phate, we prefer to maintain thetemperature about 75 gas inlet ports B9'. 68a and the sulphatedparticles are exposed to the sulphatizing action of the gases and passedprogressively from one sulphating chamber to the next lower chamber bythe action of the rabbles secured to the rotating rabble arms 58a movingthe particles towards and into the drop holes 65a. The gases areevacuated from .the sulphating chambers through the conduit 59. Thevolume of the gases admitted to and evacuated fromll the sulphatingchambers being regulated by the valves 21 and 60 respectively; It willbe apparent that variations-in our process and apparatus may be made,such as illustrated above, without departing from the scope of ourinvention.

Having thus fully described our invention', what we claim as new anddesire to secure by Letters Patentisz v 1. An improved apparatus forroasting mineral-sulphides to eifect ,a positive control over the amountof sulphates and sulphur in the nal product. which comprises a furnacehaving Ia. combustion chamber of large cross sectional area to permitthe thorough dispersal of finely divided particles, and of a depthsufilcient to permit the oxidation of suchparticles in gaseoussuspension; means for dispersing the particles with a regulated quantityof air in the upper part of the combustion chamber a settling ,hearth inthe lower part of the combustion chamber on which the suspendedparticles eventually settle and rabbling means for agitating saidparticles on the settling hearth; a main gas conduit communicating withthe combustion chamber through which the gaseous products of combustionmay be evacuated and a valve member in the conduit for controlling therate of evacuation of the gases; dust-collecting means for separatingthe dust particles from the evacuated gases; a sulphating chamber indirect communication and contiguous with the combustion chamber and asulphate settling hearth at the lower -part of the sulphating chamber;means for diverting regulated amountsof the :roasted product of thecombustion chamber into the sulphating chamber to settle on the sulphatesettling hearth; means for introducing regulated amounts of hot sulphurdioxideA bearingY gases into the sulphating chamber; conveying means forreturning regulated amounts of the dust particles separated from theevacuated gases; to the sulphating chamber; a conduit for evacuating thegases from the sulphating chamber; rabbiing means for agitating theparticles settling on the sulphate settling hearth and meansv forseparately evacuating the sulphated product from the sulphating chamber.

2. An improved apparatus for roasting mineral sulphides to eilect apositive control over the amount of sulphates and sulphur in the iinaiproduct which comprises a furnace having :a combustion chamber of largecross sectional area to permit the thorough dispersal of finely dividedaosaaoe i* y y r particles 'and or 'a depth aimaient to permit theoxidation of such particles in gaseous suspension; means for dispersingthe particles with a regulated quantity of air in the upper Dart of thecombustion chamber a settling hearth in the lower part of the combustionchamber on which the suspended particles eventually settle and rabblingmeans for agitating said particles on the settling hearth; a main gasconduit communicating with the combustion chamber through which thegaseous products of combustion may 4be evacuated and a valve member; forcontrolling the rate of such evacuation; dust-collectingl means forseparating the dust particles from the evacuated gases; a sulphatingchamber in direct communication a'nd contiguous with the combustionchamber and a sulphate settling hearth in the lower part of thesulphating chamber; means for introducing regulated amounts of theroasted product of the combustion chamber into the sulphating chamber tosettle on the sulphate settlinghearth; mea for introducing regulatedamounts of hot sulphur dioxide bearing gas formed in the combustionchamber by the combustion of the sulphur'content of the charge into thesulphating chamber and thereby maintaining the temperature of thatchamber within desired limits; conveying means for returning regulatedamounts of the dust particles separated from the evacuated gases to thesulphating chamber; a gas conduit .communicating with the sulphatingchamber and the main gas conduit and a valve member to regulate the rateof the evacuation of the gases from` the sulphating chambertherethrough; rabbling means to agitate and expose the particles on the,sulphate settling hearth to the sulphatizing action of the sulphurdioxide bearing gas and means for separately evacuating the sulphatedproduct.l

3. In combination'with a process for theroasting of mineral sulphides ingaseous suspension the method of separately evacuating the solid andgaseous Iproducts of the roasting step; separating the dust particlesfrom the evacuated gases; introducing regulated amounts of the dustparticles into a sulphating chamber in direct communication andcontiguous with the roasting step wherein they are exposed to thesulphatizing action of hot sulphur dioxide bearing gases; maintainingthe temperature of the sulphating chamber below the decompositiontemperature of the sulphates formed and separately evacuating thesulphated product and the sulphur dioxide bearing gas.

4. In combination with apparatus for the roasting of mineral sulphidesin gaseous suspension, a sulphating chamber in direct communication andcontinguous with the' roasting chamber and having a settling hearth atthe lower part thereof means for introducing regulated amounts of hotsulphur dioxide bearing gas into -the sulphatingchamber; means forintroducing regulated amounts of the roasted particles into thesulphating chamber to settle on the settling hearth; means f oragitating the settled particles; means for controlling the temperatureof the sulphating chamber below the decomposition tern perature of thesulphates formed; and means for separately evacuating the sulphatedproduct and the sulphur dioxide bearing gas.

5. In combination with apparatus for the roasting of mineral sulphidesin gaseous suspension. means for separately evacuating the solid andgaseous products of the roasting chamber; dust-collecting means forseparating the dust particles from the evacuated gases; a sulphatingchamber having a settling hearth at the lower part thereof, saidsulphating chamber in direct communication and contiguous with theroasting chamber of the roasting apparatus; conveying means forintroducing regulated amounts of the dust particl into the sulphatingchamber to settle on the settling hearth; means for introduclngregulated amounts of hot sulphur dioxide bearing gases from the roastingchamber into the sulphating chamber; rabbling means for agitating theparticles on the said settling hearth; means for controlling thetemperature of the sulphating chamber below thedecomposition temperatureof the sulphates formed; and means for separately evacuating thesulphated product and the sulphur dioxide gas.

6. In combination with apparatus for the roasting of mineral sulphidesin gaseous suspension, meansfor separately evacuating the solid andgaseous products of the roasting chamber; dust-collecting means forseparating the dust particles from the evacuated gases; a sulphatingchamber having a settling hearth at the lower part thereof, saidsulphating chamber in direct communication and contiguous with theroasting chamber of the roasting apparatus; means for introducingregulated amounts of the solid products of the combustion chamber intothe sulphating chamber to settle on the settling hearth thereof; conduitmeans for introducing regu.'-

lated amounts of hot sulphur dioxide bearing gas from the roastingchamber into the sulphating chamber; rabbling means for agitating theparticles on the said sulphate settling hearth; means ior controllingthe temperature of the sulphating chamber below the decompositiontemperature of the sulphates formed; and means for separately evacuatingthe sulphated product and the sulphur dioxide bearing gas.

'7. In combination with a process for the roasting of mineral sulphidesin gaseous suspension the method of separately evacuating the solid andgaseous products of the roasting step; separating the dust particlesfrom the evacuated gases; introducing regulated amounts of the dustparticles into a sulphating step in direct Acommunication and contiguouswith theroasting step of the process wherein they are exposed to thesulphatizing action of sulphur dioxide bearing gas; maintaining thetemperature of the sulphating step below the decomposition temperatureof the sulphates formed by directing into the sulphating step regulatedamounts of hot sulphur dioxide bearing gas from the combustion step andseparately evacuating the sulphated product and the sulphur dioxidebearing gas.

BYRON ANGUS STIMMEL. KENNETH DUNCAN McBEAN. GRAHAM CRUICKSHANK.

